The preparation of tissue samples for histological examinations takes place by way of several chemical treatments and by a final embedding of the sample in paraffin. During the chemical treatment, the sample is first fixed with a suitable chemical liquid, then the water contained in the sample is extracted and replaced by stabilizing agents, coloring agents and the like. Finally, the sample is embedded in paraffin or wax. What is achieved hereby is that a paraffin block can be kept stable in a receptacle of a microtome for cutting individual thin tissue sections. For different successive methods steps, so-called tissue infiltration devices or embedding machines have been developed, which automatically transport the samples into the different treatment stages.
The sample can be a biopsy, a punch or a tissue part removed during a surgery. These samples are each placed in a cassette, in which they are transported through the individual treatment steps. Merely exemplarily, the document DE 103 42 264 A1 is mentioned in which, inter alia, such a cassette is described. Eventually, these samples or thin tissue sections thereof are to be subjected to a histological examination. To this end, a pathologist observes with the aid of a microscope a sample thin section prepared with a microtome and placed on a slide, wherein the sample thin section can be dyed by means of a dyeing method and can be provided with a cover glass.
By means of the transport apparatus of the tissue infiltration device it shall in particular be possible to simultaneously transport at least two transport devices in the tissue infiltration device or to transport two transport devices that are simultaneously present in the tissue infiltration device one after the other in a time-shifted manner. By means of the transport apparatus a transport device is usually brought to a liquid container and placed into the same. By means of the transport apparatus—usually at a later point in time—the transport device is then moved out of the liquid container and away from the liquid container.
What is to be particularly understood by a sequence of operations or processing order in the sense of the present invention is that an order is predetermined or can be predetermined—for example by an operator of the tissue infiltration device —according to which a transport device with cassettes runs through the liquid containers provided in the tissue infiltration device. In this connection, a liquid container can also be considered as a processing station at which the cassettes contained in a transport device and hence the samples are brought into the liquid contained in the liquid container, as a result whereof the liquid acts on the samples. Insofar, by the expression “run through” in the sense of the present invention it is to be particularly understood:                the transport of a transport device with cassettes and hence with samples from an input station, at which a transport device is transferred to the tissue infiltration device, to the first liquid container of the sequence and into the same,        the removal from the liquid container after a predeterminable reaction time,        the transport of a transport device to the next liquid container and into the same etc., and, finally        the transport to an output or transfer station, at which a processed transport device can be output or removed from the tissue infiltration device. A transfer station could transfer a processed transport device to an auto-embedder.        
For example, from DE 196 47 662 C1, a tissue infiltration device is known in which a plurality of liquid containers are circularly arranged. To this tissue infiltration device one or, as the case may be, also more transport devices can be transferred one after the other in a time-shifted manner. These are conveyed by the transport apparatus provided therein in a predetermined sense of rotation from one liquid container to the next liquid container, wherein the transport apparatus provided therein is designed such that during one transport operation all transport devices contained in the tissue infiltration device are brought to the respective next liquid container. A complete run through of a transport device can last from one to several hours. Fully automated tissue infiltration devices can be operated automatically over night when appropriately loaded. As soon as a transport device is transferred to the tissue infiltration device a further transport device can indeed be transferred to the tissue infiltration device, but it is transported and hence processed sequentially through the individual stations or liquid containers of the tissue infiltration device in the same operational sequence as the transport device already present in the tissue infiltration device. If now the samples contained in a transport device are to be processed particularly urgently, this is not readily possible with the tissue infiltration device known from DE 196 47 662 C1 since transport devices already present in the tissue infiltration device cannot readily be removed prior to a complete run through the tissue infiltration device.
This difficulty is addressed in DE 101 63 488 A1, in which a tissue infiltration device is provided which has an additional liquid container with a smaller filling volume than the first treatment chamber. In the first treatment chamber several transport devices are processed. In the additional liquid container, a transport device can be subjected to an urgent treatment. Here, the liquid required for the respective processing step is each time filled into this liquid container and again removed after a predetermined reaction time. This indeed allows subjecting a transport device to an urgent tissue infiltration. However, it is also required, after emptying the liquid container, to first clean this liquid container before it can be filled with another liquid. This in turn is complex and requires a complex control of the filling and emptying operations of both the liquid container and the first treatment chamber. Furthermore, cleaning reagents are to be used which increase the running costs of the tissue infiltration device.